Please refer to FIG. 1, which is a circuit diagram showing a conventional voltage regulator according to the prior art. In FIG. 1, the voltage regulator includes a differential circuit 11 and a pump high-voltage circuit 12. The differential circuit 11 includes a first stage circuit and a second stage circuit. The pump high-voltage circuit 12 includes a third stage circuit and a fourth stage circuit. The pump high-voltage circuit 12 is further electrically connected to an output stage circuit.
In the first stage circuit, the respective sources of the PMOS transistors P1 and P2 are electrically connected to a high voltage source Vdd. The respective gates of the PMOS transistors P1 and P2 are electrically connected to each other. The gate of the PMOS transistor P2 is electrically connected to the drain thereof. The drain of the NMOS transistor N1 is electrically connected to the drain of the PMOS transistor P1. The gate of the NMOS transistor N1 is to receive a voltage reference signal V_Reference. The drain of the NMOS transistor N2 is electrically connected to the drain of the PMOS transistor P2. The gate of the NMOS transistor N2 is to receive a feedback signal fb. The respective sources of the NMOS transistors N1 and N2 are electrically connected to the drain of the NMOS transistor N3. The gate of the NMOS transistor N3 is to receive a voltage bias signal V_bias. The source of the NMOS transistor N3 is electrically connected to a low voltage source Vss.
In the second stage circuit, the source of the PMOS transistor P3 is electrically connected to the high voltage source Vdd. The gate of the PMOS transistor P3 is electrically connected to the drain of the NMOS transistor N1. The drain of the PMOS transistor P3 is electrically connected to the drain of the NMOS transistor N4. The gate of the NMOS transistor N4 is electrically connected to the drain thereof. The source of the NMOS transistor N4 is electrically connected to the low voltage source Vss.
In the third stage circuit, the respective sources of the PMOS transistors P4 and P5 are electrically connected to a pump voltage source Pump HV. The respective gates of the PMOS transistors P4 and P5 are electrically connected to each other. The gate of the PMOS transistor P4 is electrically connected to the drain thereof. The drain of the NMOS transistor N5 is electrically connected to the drain of the PMOS transistor P4. The gate of the NMOS transistor N5 is electrically connected to the gate of the NMOS transistor N4. The source of the NMOS transistor N5 is electrically connected to the low voltage source Vss.
In the fourth stage circuit, the drain of the PMOS transistor P5 is electrically connected to electrically series-connected resistors R1 and R2. Another end of the resistor R2 is electrically connected to the low voltage source Vss.
The output stage circuit includes a capacitance load Cload. One end of the capacitance load Cload is electrically connected to a node between the drain of the PMOS transistor P5 and the resistor R1 to be the output terminal output, and another end of the capacitance load Cload is electrically connected to the low voltage source Vss.
Please refer to FIG. 2, which is a graph showing the output terminal voltage of the voltage regulator and the currents of the PMOS transistors P4 and P5 according to FIG. 1. When the capacitance load Cload is charged, the voltage level of the output terminal output is still low. The feedback signal fb is then raised to be close to the voltage reference signal V_Reference. The voltage of the node A is low, and the voltage of the node B rises from a low point. The voltage of the node B being at the high point will cause the voltage pbias of the node C to go low, and the current I2 of the PMOS transistor P5 is thus increased.
Besides, the current I1 of the PMOS transistor P4 is increased since the voltage pbias of the node C is low. The currents I1 and I2 are both provided by the pump voltage source Pump HV. For the increase of the currents I1 and I2 leads to the complex design and the poor current efficiency of the pump voltage source.